This invention relates to the generation of high-density plasma, particularly inductively coupled plasma (ICP), useful in processes such as semiconductor wafer processing.
Gas plasma generation is widely used in a variety of integrated circuit (IC) fabrication processes, including plasma etching, plasma enhanced chemical vapor deposition (PECVD), and plasma sputter deposition applications. Generally, plasmas are produced within a process chamber by introducing a process gas at vacuum pressure into the chamber and then coupling electrical energy into the chamber to create and sustain a plasma in the process gas. The plasma may exist a t various ionization fractions from 10xe2x88x926 to a fully ionized plasma.
The plasma generally contains positively charged ions of working gas that are used for etching a surface of a substrate, sputtering material from a target for depositing a layer of the material onto such a substrate and ions of vaporized coating material to control the deposition of the material onto the substrate by ionized physical vapor deposition (iPVD). The plasma typically contains electrons equivalent in number to the positive charges in the plasma so that the plasma is macroscopically quasi-neutral.
Various ways of producing a plasma within a process chamber are used. Opposed electrodes can be oriented within the chamber to capacitively couple energy to the plasma. Microwave energy and electron cyclotron resonance (ECR) devices are also used. Inductive coupling of energy to the plasma is particularly desirable for producing a high-density plasma, particularly plasmas having a high ionization fraction with a relatively low electron energy or plasma potential. Inductively coupled plasmas (ICP) often use a coil or antenna-shaped and positioned with respect to the processing chamber to inductively couple energy into the processing chamber and thus create and sustain a plasma therein.
In some ICP systems, an inductive coil or antenna is positioned proximate the top portion of the chamber to create a plasma within the chamber. The antenna is positioned on one side of a dielectric plate or window at the top of the processing chamber, and electromagnetic energy from the antenna is coupled through the dielectric window and into the plasma. One such design is illustrated in U.S. Pat. No. 5,556,521. In other ICP systems, helical or solenoidal-shaped coils are wound around the outside of a cylindrical dielectric sidewall of the processing chamber to inductively couple energy to the plasma. One suitable dielectric material for a window or chamber sidewall is quartz.
The geometry of an ICP system is a factor in determining both plasma density and uniformity, which, in turn, can affect the processing uniformity over the area of the substrate. It is usually desirable to produce a uniform, high-density plasma over a significantly large area so that large substrate sizes can be accommodated. Ultra large-scale integrated (ULSI) circuits, for example, are presently formed on wafer substrates having diameters of 200 mm and 300 mm.
In an ICP system, plasma is excited by heating or exciting electrons in the plasma region of the processing chamber. The inductive currents which heat the plasma electrons are der iv ed from oscillating magnetic fields which are produced proximate the inside of the dielectric window or sidewall by RF currents within the inductive antenna or coil. The spatial distribution of those magnetic fields is a function of the sum of the individual magnetic fields produced by each portion or segment of the antenna or coil conductor. Therefore, the geometry of the inductive antenna or coil significantly determines the spatial distribution of the plasma, and particularly the spatial distribution and uniformity of the plasma ion density within the process chamber. Some coil configurations achieve a goal of delivering power linearly over a wide power range within a chamber of a given radius, but it is difficult to scale the process chamber to a larger size for handling larger substrates without significantly increasing the dimensions of the antenna or coil. Replacing an ICP antenna with one of a larger footprint calls for expensive modification to the processing system, and larger antennas and their associated plasmas exhibit greater sensitivity to process parameters within the chamber. For example, with a larger antenna, the plasma process becomes more sensitive to substrate-to-target distance, the target material, the pressure within the process chamber, and the height and width configuration of the chamber. Furthermore, large coils call for large dielectric windows, which must be very thick to withstand the pressure differential across the wall of a high vacuum chamber.
Current ICP systems utilizing planar spiral antennas exhibit asymmetry wherein the distribution of the plasma that is not aligned with the central axis of the chamber, which degrades the uniformity of the deposition or etch process over the area of the substrate. Further, planar antennas often exhibit a ring or doughnutshaped plasma for one process and corresponding set of parameters, while creating a centrally peaked plasma for another process and other parameters. Accordingly, the plasma shape and uniformity is not consistent within such ICP systems and will be process dependent. Therefore, the overall IC fabrication process will not be consistent from one plasma process to another plasma process.
Another drawback of planar antenna systems using an S-shaped coil is that the outer portions of the coil marginally affect the plasmas created by the central region of the coil and give an effect on the uniformity and density of the plasma that is different along one axis of the plane of the coil than along another axis in the plane of the coil.
An objective of the present invention is to overcome drawbacks in the prior art and provide a plasma processing system, particularly an ICP system, in which a dense, uniform plasma is created. Another objective of the present invention is to provide a uniform plasma that is less dependent upon the size and shape of the process chamber than current plasma processing systems. Still another objective of the invention is to provide a plasma that is symmetrical in the processing chamber.
A further objective of the present invention is to provide a uniform, dense plasma over a large area, such as an area sufficient to handle 200 mm and 300 mm wafers, while maintaining a compact and inexpensive design of the inductive coil or antenna. A still further objective of the present invention to provide consistent plasma generation and thereby provide consistent processes that are less dependent upon process parameters such as pressure and chamber geometry or size.
According to principles of the present invention, a high-density, inductively coupled plasma (ICP) producing source is provided for coupling RF energy into a vacuum processing chamber. The source includes a window of a dielectric material in the chamber wall and having a surface in contact with a processing gas within a vacuum processing chamber. An RF antenna in the form of a coil is isolated from the processing gas by the dielectric material and has first coil segments, preferably lying in a plane parallel to the window, extending circumferentially in a ring close to the surface of the window. A permanent magnet assembly is configured and positioned to generate a ring-shaped magnetic tunnel in the processing chamber near the surface of the dielectric material in a ring-shaped area opposite the window from the coil segments.
In preferred embodiments of the invention, the RF coil is a three-dimensional coil having further second coil segments extending farther from the surface of the window than those extending in the ring. The further segments preferably lie in planes that intersect the dielectric material. Preferably, the half turn segments close to the window include two pairs of segments. The turns of each pair extend around the ring so that current flows in opposite directions, one clockwise and one counterclockwise.
The preferred coil is formed of segments of a single hollow conductor having a cooling fluid passage therein, with the segments connected in series across an RF power generator. The order of the segments preferably is: a clockwise extending first segment, then a second segment, then a clockwise extending first segment, then at least one segment, then a counterclockwise extending first segment, then a second segment, then a counterclockwise extending first segment.
In certain embodiments, at least three of the second coil segments are provided, with the segments arranged as: a clockwise extending first segment, then a second segment, then a clockwise extending first segment, then at least one second segment, then a counterclockwise extending first segment, then a second segment, then a counterclockwise extending first segment. In some such embodiments, the coil includes only seven segments, including the three curved second segments and two pairs of the first segments, arranged with no other intervening segments. In other such embodiments, other segments may be included.
In other embodiments, the coil includes a plurality of the curved second segments, at least two pairs of the first segments and at least one relatively straight intermediate segment lying in t he plane containing the pairs of first segments. Preferably, the segments are arranged as: a clockwise extending first segment, then a second segment, then a clockwise extending first segment, then an intermediate segment, then a counterclockwise extending first segment, then a second segment, then a counterclockwise extending first segment. In some such embodiments, the coil includes only seven segments, including the two curved second segments, two pairs of the first segments and one relatively straight intermediate segment lying in the plane containing the pairs of first segments and oriented such that magnetic field lines encircling the intermediate segment in a plane perpendicular thereto circulate in a direction opposite magnetic field lines encircling the first segments in the same plane, with the segments arranged as: a clockwise extending first segment, then a second segment, then a clockwise extending first segment, then the intermediate segment, then a counterclockwise extending first segment, then a second segment, then a counterclockwise extending first segment. In other such embodiments, other segments may be included.
For example, a coil that has a plurality of the curved second segments, at least two pairs of the first segments and at least one relatively straight intermediate segment lying in the plane containing the pairs of first segments, may include a plurality of at least four curved second segments, at least two pairs of the first segments and at least one relatively straight intermediate segment lying in the plane containing the pairs of first segments and oriented such that magnetic field lines encircling the intermediate segment in a plane perpendicular thereto circulate in a same direction as magnetic field lines encircling the first segments in the same plane, with the segments arranged as: a clockwise extending first segment, then a second segment, then a clockwise extending first segment, then a second segment, then an intermediate segment, then a second segment, then a counterclockwise extending first segment, then a second segment, then a counterclockwise extending first segment. In one such other embodiment, the coil includes four curved second segments, two pairs of the first segments and one such relatively straight intermediate segments.
In various embodiments, the plasma producing source includes a Faraday shield inside the chamber, closely spaced from, and generally parallel to, the dielectric material. The shield has a plurality of slots therethrough immediately opposite the dielectric material from the first segments. The slots include slots that lie in planes generally perpendicular to the first segments, and preferably that lie immediately opposite the dielectric material from the ring and oriented in a generally radial direction. Where intermediate segments are provided, slots are included immediately opposite the dielectric material from the each intermediate that lie in planes generally perpendicular to the intermediate segments.
The permanent magnet assembly preferably includes an inner magnet having a generally circular outer perimeter forming a first pole spaced radially inward of the ring and an annular outer magnet having an inner perimeter forming a second pole, the magnetically opposite of the first pole, spaced radially outward of the ring. The permanent magnet assembly may be located in various positions, one, for example, being adjacent the dielectric material outside of the chamber and another being adjacent, for example, embedded within, the shield.
The source is useful in an etching apparatus in combination with the vacuum chamber having a substrate support within the chamber. Alternatively, the source is further useful in an iPVD apparatus in combination with the vacuum chamber having a substrate support within the chamber that is further equipped with a magnetron sputtering cathode for sputtering material into a region within the chamber containing the high-density inductively coupled plasma.
RF antennae for inductively coupling energy into a vacuum processing chamber for sustaining a high-density plasma formed of the coils described herein are also provided by the invention. Faraday shields for use with RF antenna are also provided by the invention. Such shields include a conductive metal disc having a plurality of slots therethrough in a concentric annular area and oriented in the annular area in a generally radial direction and may include slots therethrough in a central area within the annular area. For deposition applications, particularly those involving coatings of metal, the slots are preferably angled, such as in a chevron shape or Z-shape, so as to prevent line-of-sight paths for particles of coating material moving from the plasma onto the dielectric material.
The plasma source of the invention used in etching coating applications produces a uniformity of plasma in the processing zone, and increased plasma source efficiency.
These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description.